Episode 10 – Cairo, al-Haytham and the Book of Optics
Islamic Golden Age (2017)
By Eamon Gearon
Film Review
Al-Haytham’s seven volume Book of Optics was published between 1011 and 1021 AD. The Cairo scholar was on house arrest at the time for failing to build an effective hydraulic system to control the Nile’s annual floods. The Fatamid caliphate had successfully won independence from the Abbasid caliphate in 969 AD, making Cairo Egypt’s capitol for the first time. The Fatamids’ massive international trade in agricultural produce enabled its leaders to become very rich.
In 1005 AD al-Hakim, the sixth Fatimid caliph, established his own Shia Islam intellectual center in Cairo. It’s library featured 200,000 volumes, 18,000 of them books on math, chemistry, medicine and astronomy. The Sunni Abassid caliphate viewed them as heretics, which hard to attract Sunni Muslims scholar without major financial incentives.
Al-Haytham was born in Basra (in modern day Iraq) ruled by the Buyids, a Persian Shia regime that had also broken away from the Abassid caliphate. He was a polymath with advanced skills in geometry, meteorology, astronomy and optics. He published a total of 100 books, with 25 on math and number theory and 45 concerning physics, chemistry and geology. He also supported himself by translating ancient Greek texts into Arabic.
Some of his more famous titles include
- On the Nature of Shadows
- Horizontal Sundial
- Rainbows and Halos
- Squaring the Circle
- On the Light of the Moon (from the Sun)
He was also the first scholar to offer an explanation why the sun and moon appear larger when they’re closer to the horizon (something that also troubled Aristotle and Ptolemy). His “moon illusion” (also known as SDIH or Size Distance Invariance) is the most commonly accepted theory today.
Al Haytham is also viewed as the father of scientific inquiry. Although the ancient Greeks accepted the importance of empirical data and experimentation in explaining natural phenomenon, they often offered a “theory of proof” instead (ie using logic to draw conclusions from arbitrary philosophical premises).
In the area of optics, the Greeks had two conflicting theories explaining how the eye worked. Euclid and Ptolemy believed in emission theory, which postulated that eye sent out rays of light. Aristotle believed in intromission theory, that observed physical forms somehow entered the eye.
A medical practitioner specializing in eye ailments, al-Haytham expanded Galen’s work on the anatomy of the eye and removed cataracts from patients’ eyes via needle suction.
Of his seven volume Book of Optics, three volumes deal with refraction, with two volumes devoted to refraction experiments, demonstrating the effect of lenses and mirror on the behavior of light. He also conducted numerous experiments with a camera obscura (which he invented) 500 years before DaVinci introduced it in the West.
Al-Haytham used it to demonstrate that the light from an image that passes through through the pinhole in a camera obscura projects an upside down version of of the object inside.
Vitello’s 13th century investigations into perspective were strongly influenced by al-Haytham, as were Kepler’s, Newton’s and Galileo’s optics experiments.
Al-Haytham challenged Ptolemy’ view that the sun and stars travel around the earth but couldn’t prove it.
Following the Fatamid empire’s conquest by the Kurdish leader Saladin in 1171, al-Haytham’s books traveled to Andalusia, where at the end of the 13th century they were translated into Latin and Hebrew.
The Most Revolutionary Act 